This invention relates to improved lubricating oils and particularly concerns automobile and Diesel crank-case lubricating oil formulations containing a minor amount of a new class of oil-soluble addition agents which improve the performance of the oil, particularly its dispersant-detergent function thus enabling lubricating oils to provide a high degree of protection of the lubricated parts of internal combustion engines.
Present-day automobile and Diesel engines have been designed for higher power output, lower combustion products emission and longer in-service periods of use of crankcase lubricating oils. These design changes have resulted in such severe operating conditions as to necessitate devising higher efficiency lubricating oils that will, under the increased severity of in-service use, afford proper protection against corrosion and the accumulation or deposition of sludge, varnish and resinous materials on the surface of engine parts which rapidly accelerate decrease in both operating efficiency and life of the engine. The principal ingredient of crankcase lubricants is a base lubricating oil, a mixture of hydrocarbons derived from petroleum. Even when highly refined by removal of deleterious components, such as polymerizable components, acid formers, waxes, etc., a lubricant base oil still requires the addition of a number of oil-soluble chemical additives to enable the oil to resist oxidation, deposition of sludge and varnish on, and corrosion of, the lubricated metal parts, and to provide added lubricity and regulated viscosity change from low to high temperature. These ingredients are commonly known as anti-oxidants, dispersant-detergents, pour point dispersants, etc.
Combustion products from the burning of fuel and thermal degradation of lubricating oils and addition agents tend to concentrate in the crankcase oil with the attendant formation of oil-insoluble deposit-forming products, that either surface coat the engine parts (varnish or lacquer-like films) or settle out on the engine parts as viscous (sludge) deposits or form solid ash-like or carbonaceous deposits. Any of such deposits can restrict, and even plug, grooves, channels and holes provided for lubricant flow to the moving surfaces of the engine requiring lubrication thus accelerating the wear and thus reducing the efficiency of the engine. In addition, acidic combustion products corrode the lubricated metal surfaces. Chemical additives are blended in crankcase oil formulations not only to reduce thermal decomposition of the oil and addition agents (anti-oxidants) but also to keep in suspension (as a dispersant) and to resuspend (as a detergent) insoluble combustion and degradation products as well as to neutralize acidic products (anti-corrosion agents). A separate additive is usually added for each improvement to be effected.
Various ingredients have been developed for the purpose of providing the dispersant-detergent function. Neutral and overbased metallo-organic compounds, such as the alkaline earth metal salts of sulfonic acids and hydrocarbon-P.sub.2 S.sub.5 reaction products were the first addition agents used for this purpose. Their in-service drawbacks included the formation of metal-ash thermal decomposition products which deposited on engine parts; they could not efficiently disperse or resuspend lacquer or varnish formers or sludge formers; and they lost their dispersant-detergent function when their alkaline earth metal component had been consumed in neutralizing acidic products of combustion.
As performance levels increased and the recommended periods between oil drains lengthened for both automobile and railway Diesel engines, more efficient dispersancy and detergency performance as well as acid neutralization and lower ash-forming tendency were demanded for lubricating oil formulations. During the past several years, a great deal of time and effort has been directed at providing addition agents for lubricants capable of satisfying such performance demands. When high molecular weight polybutene polymers became commercially available in the early 1940's, research workers in various laboratories devised, for this dispersant-detergent function, a series of derivatives of polybutene-phosphorus pentasulfide reaction products, e.g., alkaline earth metal salts, alkylene polyamine and alkylene oxide derivatives, in which the high molecular weight of the polybutene group greatly enhanced their effectiveness. Other devised amine salts, amides, imides and amidines of polybutenyl-substituted polycarboxylic acids and polymeric compounds having pendant or grafted-on polar groups. Still other suggested combinations of alkaline earth metal sulfonates and Mannich condensation products of a low molecular weight alkyl (C.sub.2 -C.sub.20) substituted hydroxyaromatic compound, an amine having at least one replaceable hydrogen on a nitrogen and an aldehyde and alkaline earth metal salts (phenates) of those Mannich condensation products but without notable success. The latter compositions still possessed the objectionable feature of forming harmful metal-ash deposits, and were incapable of providing the increased dispersancy-detergency service demanded for long drain service of present-day engine requirements.
Mannich condensation products derived from alkyl-substituted hydroxyaromatic compounds having a relatively low molecular weight alkyl substituent, i.e., 2 to 20 carbon atoms in the alkyl substituent and chlorinated wax (straight chain) type alkyl-substituents are described in U.S. Pat. Nos. 2,403,453; 2,353,491; 2,363,124; 3,459,112; 2,984,550 and 3,036,003. However, none of such prior Mannich condensation products are suitable for use as dispersant-detergent addition agents for present-day long drain oil interval in-service use.
One known type (U.S. Pat. No. 2,363,134) has been prepared by reacting, under Mannich reaction conditions, equimolar quantities of a C.sub.2 -C.sub.20 alkyl-substituted phenol and other hydroxy aromatic compounds, and N,N-di-substituted amine and formaldehyde according to the following equation: ##STR1## wherein R is an alkyl group having between 2 and 20 carbon atoms and R.sub.1 and R.sub.2 may be alkyl, cycloalkyl, aryl or arakyl radicals.
Other prior low molecular weight Mannich condensation products formed by condensing a C.sub.2 to C.sub.20 alkyl-substituted phenol, an alkylene diamine and an aldehyde in the respective molar ratios of 2:1:2, have been illustrated by the following structural formula: ##STR2## wherein R is a divalent alkylene hydrocarbon radical and R.sub.1 is an alkyl group containing from 2 to 20 carbon atoms.
Still others have been prepared by reacting C.sub.2 -C.sub.20 alkylphenols, formaldehyde and alkylene polyamines of the formula ##STR3## wherein A is a divalent alkylene radical of 2 to 6 carbon atoms and n is an integer from 1 to 10, in the ratio of from 0.5 to 2 moles each of C.sub.2 -C.sub.20 alkylphenol and formaldehyde for each nitrogen group contained in the alkylene polyamine reagent. The molar reactant ratio range of C.sub.2 -C.sub.20 alkylphenol, amine and formaldehyde used to form such products is 1-20:1.0:1-20. U.S. Pat. No. 3,036,003 exemplifies such products, which usually are formed with ethylene polyamines, according to the above formula in which A is --CH.sub.2 --CH.sub.2 -- and N is 2, 3 and 4. For example, reaction of p-tertiary octylphenol, diethylene triamine, and formaldehyde in the respective molar ratios of 3:1:3 is illustrated in said patent as N.sub.1, N.sub.2, N.sub.3 -tri-(2-hydroxy-5-t-octylbenzyl) di-ethylene triamine and the reaction of the aforesaid reactants in the respective molar ratios of 2:1:2 is illustrated as being either N.sub.1, N.sub.3 or N.sub.1, N.sub.2 -di-(2-hydroxy-5-t-octylbenzyl) diethylene triamine.
The foregoing prior C.sub.2 -C.sub.20 alkyl-substituted Mannich condensation products commonly are prepared by the conventional technique of adding the aliphatic aldehyde to a heated mixture of the alkylhydroxyaromatic and amine reagents, in the presence or absence of a solvent, and then heating the resultant mixture to a temperature between 100.degree.-350.degree. F. until dehydration is complete. A solvent such as benzene, toluene, xylene, methanol and others easily separated from the reaction mixture are light mineral oils, such as those used in blending stocks to prepare lubricating oil formulations in which the product is formed as a mineral oil concentrate are usually used. The water by-product is removed by heating the reaction mixture to a temperature sufficiently high, at least during the last part of the process, to drive off the water alone, or as an azeotropic mixture with the aromatic solvent, usually by the aid of an inert stripping gas, such as nitrogen, carbon dioxide, etc.
The exactly neutralized or overbased alkaline earth metal salts (alkaline earth metal phenates) of those prior low molecular weight Mannich condensation products have been suggested for use in providing lubricating oils with a combination of detergent-inhibitor properties in one addition agent. The exactly neutralized alkaline earth metal salts have one equivalent of alkaline earth metal for each hydroxy group present. The overbased salts have, for each hydroxy group present, more than one equivalent of alkaline earth metal in the form of a hydroxy metaloxy, alkoxy metaloxy and even alkaline earth metal carbonate complex with hydroxy metaloxy on each benzene group as a replacement for the phenol hydroxy group. As noted above, said addition agents form objectionable metal ash deposits and have other performance deficiencies.
Certain hydroxy C.sub.2 -C.sub.20 alkylbenzyl substituted ethylene polyamines have been suggested, in U.S. Pat. No. 3,036,003, as being useful per se in lubricating oil formulations of ashless-type detergents. The product resulting from the reaction of p-tertiary-octylphenol, tetraethylene pentamine and formaldehyde in a molar reactant ratio of 4:1:4, characterized as the tetra-(hydroxy-5-tertiary-octylbenzyl) derivative of tetraethylene pentamine is indicated, by said patent, as capable of imparting detergency to lubricating oils on the basis of a carbon black suspension test described in the patent. However, that patent itself demonstrates, by an oxidation stability test, that the very same product is a lubricating oil formulation, with no other detergent added, permits sludge and varnish formation as well as oxidation of the base oil. Thus, U.S. Pat. No. 3,036,003 demonstrates that its Mannich condensation products, when added as the sole detergent agent in a lubricating oil, are incapable of providing a satisfactory level of detergency and are also incapable of inhibiting oxidation of the base oil.
U.S. Pat. No. 3,235,484 issued February 15, 1966 (now Reissue No. 26,330) describes the addition agents of certain disclosed compositions to refinery hydrocarbon feed stocks for the purpose of inhibiting the accumulation of carbonaceous deposits in refinery cracking units. The primary inhibitors disclosed are mixtures of amides, imides and amine salt formed by reacting an ethylene polyamine with hydrocarbon substituted succinic acids or anhydride, whose hydrocarbon substituent has at least about 50 carbon atoms. As an adjunct for such primary carbonaceous depost inhibitors there is disclosed in said patent Mannich condensation products formed by reacting (1) alkylphenol, (2) an amine and (3) formaldehyde in the ratio of one mole alkylphenol and from 0.1-10 mole formaldehyde for each active nitrogen group contained in the amine reactant. Alkylphenols whose alkyl group has a molecular weight as high as 50,000 and contains from monoalkylphenols whose alkyl group contains 4-30 carbon atoms are stated to be the preferred alkylphenol reactants.